Field-Scale Salt and Water Balance during Integrated Seawater Farming in Coastal Regions of Abu Dhabi

Halophyte agriculture using seawater offers a sustainable solution for the generation of biomass feedstock for carbon‐neutral biofuels. Long‐term irrigation of crops with saline water poses several challenges to soil productivity, such as increased soil sodicity and salinity. While amending sodic soils with gypsum and biochar has been widely practiced, its applicability in seawater agriculture has not been previously investigated. In this project, continuous‐flow packed‐column experiments were carried out using seawater. In addition, a 1‐D reactive transport geochemical model was developed and validated using the temporal dissolution profiles of gypsum in seawater.

Finally, a sensitivity analysis of the model was conducted, as well as predictive modeling exercises to assess site‐specific parameters such as feed water options and coastal soil type and their impact on evaporative mineral precipitation and agricultural return water quality. From the column experiments, it was observed that a three times increase in the soil gypsum amendment weight fraction resulted in more than four times increase in time for complete elution. Furthermore, the measured SAR values for gypsum‐amended soils after 25 pore volumes of displacement were only 33‐50% higher than in soils where native halophytes grow. Further amendment of gypsum amended soils with 1% by weight of biochar resulted in increased calcium retention in the soil.

Model validation and sensitivity analysis identified longitudinal dispersivity and the gypsum dissolution rate constant as the most sensitive parameters to the geochemical model. Activity coefficient models tested showed the most significant discrepancy in return water salinity for gypsic soils, possibly explaining the residual error in model validation. Note that the scope of the project was modified from the originally proposed field‐scale project to one involving mathematical modeling and laboratory experiments because of the unavailability of the field site over the project duration.